package demo2;

class Solution {
    public String toLowerCase(String s) {
        if(s == null || s.length() ==0) {
            return null;
        }
        StringBuilder sb = new StringBuilder();
        for(int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            if(ch >= 'A' && ch <= 'Z') {
                sb.append((char)(ch+32));
            }else {
                sb.append(ch);
            }
        }
        return sb.toString();
    }
    
}